Fall 2009 Issue

VHF PROPAGATION

The Verdict is Still Out

By Tomas Hood,  NW7US

Figure 2. The “intensitygram” of the Sun using the Michelson Doppler Imager (MDI) on September 23, 2009, showing the two active sunspot regions, 1026 and 1027. August 2009 was void of any spots, leaving many to again speculate that we are in a Maunder Minimum. These sunspots in September seem to counter such speculations. (Source: SOHO)

A year ago we discussed the possibility that the Sun was entering another Maunder Minimum, which occurred during the period starting in 1645 and ending in 1715, an incredible 70 years during which sunspots were rarely seen. To the observer, this period is void of evidence of any 11-year solar cycles. What’s more, this period coincided with the infamous “Little Ice-Age,” a series of extraordinarily cold winters in the Northern Hemisphere. During the year since we discussed the above possibility, the Sun has not presented much sunspot activity, leading many to yet postulate that we are indeed seeing a possible extended period of solar quiet, perhaps lasting years.

As was demonstrated in this column last year and during the time since then, the sunspots now occurring predominantly belong to the new cycle, as they have the magnetic orientation consistent with the expected reversal from those spots of the old sunspot Cycle 23. However, these new sunspots are few and far between.

After the appearance of a series of very small sunspots during July 2009, the entire month of August was quiet; not one sunspot was observed. This places August as the month with the lowest observed monthly sunspot activity between sunspot Cycles 23 and 24. This fact will move the statistical solar minimum later than December of 2008.

During September 2009, while most days were spotless, two significant sunspot regions developed and lasted for days (figures 1, 2, and 3). One of the regions even produced a moderate solar flare on September 25th. All of this activity started on September 21st as the first sunspot region rotated into view. The next day a second region appeared. Both sunspots grew larger, causing the 10.7-cm flux to peak at 76 on the 23rd. These two regions indicate that the new cycle is picking up energy, although the increase in activity is much slower than we’ve observed in past cycles.

Unprecedented Opportunities

Have there been any interesting discoveries in the world of VHF propagation during this extended period of solar quiet? Art Jackson, KA5DWI, has been studying sporadic-E (Es) propagation for the last five years by using data collected from the PropNET project (http://www.propnet.org/). Regarding the 2009 Es season, he observes, “The year was phenomenal. I think the best we have had of the past 5 years. What made it special was that 10 meters was open on average 3 hours more each day this season. Some weeks were as much as 6 hours better.” He also observes that 6-meter openings were just as reliable and frequent.

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